Zooming an SKNode inconsistent

Question

I have created my own solution for zooming in or out on a specific SKNode without having the zoom the entire scene, and it seems to work mostly how I would expect it to work, with 2 notable exceptions which I am hoping to get input on here. First the code (this control statement is within the touchesMoved method):

 if (touches.count == 2) {
        // this means there are two fingers on the screen
        NSArray *fingers = [touches allObjects];
        CGPoint fingOneCurr = [fingers[0] locationInNode:self];
        CGPoint fingOnePrev = [fingers[0] previousLocationInNode:self];
        CGPoint fingTwoCurr = [fingers[1] locationInNode:self];
        CGPoint fingTwoPrev = [fingers[1] previousLocationInNode:self];

        BOOL yPinch = fingOneCurr.y > fingOnePrev.y && fingTwoCurr.y < fingTwoPrev.y;
        BOOL yUnpinch = fingOneCurr.y < fingOnePrev.y && fingTwoCurr.y > fingTwoPrev.y;

        BOOL xPinch = fingOneCurr.x > fingOnePrev.x && fingTwoCurr.x < fingTwoPrev.x;
        BOOL xUnpinch = fingOneCurr.x < fingOnePrev.x && fingTwoCurr.x > fingTwoPrev.x;

        if (xUnpinch | yUnpinch) {
            if (YES) NSLog(@"This means an unpinch is happening");
            mapScale = mapScale +.02;
            [map setScale:mapScale];
        }

        if (xPinch | yPinch) {
            if (YES) NSLog(@"This means a pinch is happening");
            mapScale = mapScale - .02;
            [map setScale:mapScale];
        }
    }

Now the problems:

1. The pinch and unpinch are not always right sometimes, and I cannot quite put my finger on when this is happening, the pinch will behave as an unpinch and vis a versa.

2. When the pinching and unpinching is scaling the SKNode correctly, it is rarely as smooth as I would like. There is a bit of jerkiness to it which I find annoying.

Can anyone suggest improvements to this method? Thanks!

Answer 1

This will solve your problem, thanks to Steffen for the hints.

- (void)didMoveToView:(SKView *)view
{
    UIPinchGestureRecognizer *precog = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(handlePinch:)];
    [self.scene.view addGestureRecognizer:precog];
}

- (void)handlePinch:(UIPinchGestureRecognizer *) recognizer
{
    //NSLog(@"Pinch %f", recognizer.scale);
    //[_bg setScale:recognizer.scale];
    [_bg runAction:[SKAction scaleBy:recognizer.scale duration:0]];
    recognizer.scale = 1;
}